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Cheng Z, Li Y, Zhu X, Wang K, Ali Y, Shu W, Zhang T, Zhu L, Murray M, Zhou F. The Potential Application of Pentacyclic Triterpenoids in the Prevention and Treatment of Retinal Diseases. PLANTA MEDICA 2021; 87:511-527. [PMID: 33761574 DOI: 10.1055/a-1377-2596] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Retinal diseases are a leading cause of impaired vision and blindness but some lack effective treatments. New therapies are required urgently to better manage retinal diseases. Natural pentacyclic triterpenoids and their derivatives have a wide range of activities, including antioxidative, anti-inflammatory, cytoprotective, neuroprotective, and antiangiogenic properties. Pentacyclic triterpenoids have great potential in preventing and/or treating retinal pathologies. The pharmacological effects of pentacyclic triterpenoids are often mediated through the modulation of signalling pathways, including nuclear factor erythroid-2 related factor 2, high-mobility group box protein 1, 11β-hydroxysteroid dehydrogenase type 1, and Src homology region 2 domain-containing phosphatase-1. This review summarizes recent in vitro and in vivo evidence for the pharmacological potential of pentacyclic triterpenoids in the prevention and treatment of retinal diseases. The present literature supports the further development of pentacyclic triterpenoids. Future research should now attempt to improve the efficacy and pharmacokinetic behaviour of the agents, possibly by the use of medicinal chemistry and targeted drug delivery strategies.
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Affiliation(s)
- Zhengqi Cheng
- Sydney Pharmacy School, The University of Sydney, Camperdown, Australia
| | - Yue Li
- Sydney Pharmacy School, The University of Sydney, Camperdown, Australia
| | - Xue Zhu
- Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, Jiangsu, China
| | - Ke Wang
- Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, Jiangsu, China
| | - Youmna Ali
- Sydney Pharmacy School, The University of Sydney, Camperdown, Australia
| | - Wenying Shu
- Department of Pharmacy, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong Province, China
| | - Ting Zhang
- Save Sight Institute, The University of Sydney, Sydney, Australia
| | - Ling Zhu
- Save Sight Institute, The University of Sydney, Sydney, Australia
| | - Michael Murray
- Discipline of Pharmacology, Faculty of Medicine and Health, The University of Sydney, Camperdown, Australia
| | - Fanfan Zhou
- Sydney Pharmacy School, The University of Sydney, Camperdown, Australia
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Thompson S, Blodi FR, Larson DR, Anderson MG, Stasheff SF. The Efemp1R345W Macular Dystrophy Mutation Causes Amplified Circadian and Photophobic Responses to Light in Mice. Invest Ophthalmol Vis Sci 2019; 60:2110-2117. [PMID: 31095679 PMCID: PMC6735810 DOI: 10.1167/iovs.19-26881] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Purpose The R345W mutation in EFEMP1 causes malattia leventinese, an autosomal dominant eye disease with pathogenesis similar to an early-onset age-related macular degeneration. In mice, Efemp1R345W does not cause detectable degeneration but small subretinal deposits do accumulate. The purpose of this study was to determine whether there were abnormal responses to light at this presymptomatic stage in Efemp1R345W mice. Methods Responses to light were assessed by visual water task, circadian phase shifting, and negative masking behavior. The mechanism of abnormal responses was investigated by anterior eye exam, electroretinogram, melanopsin cell quantification, and multielectrode recording of retinal ganglion cell activity. Results Visual acuity was not different in Efemp1R345W mice. However, amplitudes of circadian phase shifting (P = 0.016) and negative masking (P < 0.0001) were increased in Efemp1R345W mice. This phenotype was not explained by anterior eye defects or amplified outer retina responses. Instead, we identified increased melanopsin-generated responses to light in the ganglion cell layer of the retina (P < 0.01). Conclusions Efemp1R345W increases the sensitivity to light of behavioral responses driven by detection of irradiance. An amplified response to light in melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) is consistent with this phenotype. The major concern with this effect of the malattia leventinese mutation is the potential for abnormal regulation of physiology by light to negatively affect health.
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Affiliation(s)
- Stewart Thompson
- Department of Psychology, New Mexico Tech, Socorro, New Mexico, United States.,Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States.,Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States
| | - Frederick R Blodi
- Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States.,Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States.,Pediatrics, University of Iowa, Iowa City, Iowa, United States.,Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
| | - Demelza R Larson
- Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States.,Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa, United States.,Biology Department, College of St. Benedict & St. John's University, Collegeville, Minnesota, United States
| | - Michael G Anderson
- Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States.,Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States.,Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa, United States.,VA Center for Prevention and Treatment of Visual Loss, Iowa City, Iowa, United States
| | - Steven F Stasheff
- Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States.,Pediatrics, University of Iowa, Iowa City, Iowa, United States.,Unit on Retinal Neurophysiology, National Eye Institute, Bethesda, Maryland, United States.,Center for Neurosciences and Behavioral Medicine, Children's National Medical Center, Washington, DC, United States.,George Washington University School of Medicine and Health Sciences, Washington, DC, United States
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Choi KJ, Na YJ, Jung WH, Park SB, Kang S, Nam HJ, Ahn JH, Kim KY. Protective effect of a novel selective 11β-HSD1 inhibitor on eye ischemia-reperfusion induced glaucoma. Biochem Pharmacol 2019; 169:113632. [PMID: 31494147 DOI: 10.1016/j.bcp.2019.113632] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 09/03/2019] [Indexed: 02/06/2023]
Abstract
Glaucoma is one of the leading causes of preventable blindness, affecting > 2 million people in the United States. Recently, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitors were found to exert preventive effects against glaucoma. However, there is no evidence for the role of 11β-HSD1 inhibitors against glaucoma. Here, we developed a novel 11β-HSD1 inhibitor, (1R,2S,3S,5R,6S,7S)-6-(2-(6-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-methyl-1,1-dioxido-1,2,6-thiadiazinan-2-yl)acetamido)-adamantane-2-carboxamide (KR-67607) and showed its protective effects against ischemia-reperfusion-induced eye injury. We demonstrate that KR-67607 effectively reduced cortisol levels in mouse eyes and maintained the trabecular meshwork (TM) structure in the presence of transient ischemic stress. Furthermore, KR-67607 reversed the elevation of intra-ocular pressure (IOP), suggesting that the TM structure maintained by KR-67607 prevented the excessive rise in IOP that exacerbates glaucoma. KR-67607 was shown to have a higher specificity for 11β-HSD1 than carbenoxolone (CBX) in vitro. Moreover, KR-67607 reduced apoptosis and the structural disruption of TM cells. Antioxidation was the major protective pathway of KR-67607 against chemically-induced ischemia-reperfusion in TM cells and the glucocorticoid receptor (GR) was closely associated with this pathway. When TM cells undergo ischemic stress, GR is activated and then translocates to the cell nucleus where it interferes with Nrf-2-mediated antioxidant gene expression. However, when KR-67607 inhibited GR translocation, Nrf-2 was able to induce antioxidant gene transcription, which consequently, enhanced the antioxidant capacity of the cells. In conclusion, our current work describes a novel selective 11β-HSD1 inhibitor for glaucoma treatment and provides evidence of its physiological role in anti-oxidative pathways in the TM.
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Affiliation(s)
- Kyoung Jin Choi
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Yoon-Ju Na
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea; Graduate School of New Drug Discovery and Development, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea
| | - Won Hoon Jung
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Sung Bum Park
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Sein Kang
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea; Graduate School of New Drug Discovery and Development, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea
| | - Hye Jin Nam
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Jin Hee Ahn
- Department of Chemistry, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea
| | - Ki Young Kim
- Therapeutics & Biotechnology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 34114, Republic of Korea; Graduate School of New Drug Discovery and Development, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea.
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Calkins TL, DeLaat A, Piermarini PM. Physiological characterization and regulation of the contractile properties of the mosquito ventral diverticulum (crop). JOURNAL OF INSECT PHYSIOLOGY 2017; 103:98-106. [PMID: 29107658 PMCID: PMC5708170 DOI: 10.1016/j.jinsphys.2017.10.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 10/20/2017] [Accepted: 10/23/2017] [Indexed: 05/16/2023]
Abstract
In adult dipteran insects (flies), the crop is a diverticulum of the esophagus that serves as a food storage organ. The crop pumps stored contents into the alimentary canal for digestion and absorption. The pumping is mediated by peristaltic contractions of the crop musculature. In adult female mosquitoes, the crop (ventral diverticulum) selectively stores sugar solutions (e.g., nectar); proteinaceous blood meals by-pass the crop and are transferred directly to the midgut for digestion. The mechanisms that regulate crop contractions have never been investigated in mosquitoes. Here we provide the first physiological characterization of the contractile properties of the mosquito crop and explore the mechanisms that regulate crop contractions. Using an in vitro bioassay we found that the isolated crop spontaneously contracts in Ringer solution for at least 1 h and its contractions are dependent on extracellular Ca2+. Adding serotonin (5-hydroxytryptamine, 5-HT) or a membrane-permeable analog of cyclic adenosine monophosphate (cAMP) to the extracellular bath increased the frequency of crop contractions. On the other hand, adding benzethonium chloride (BzCl; a chemical that mimics the effects of myosuppressins), H-89 or Rp-cAMPS (inhibitors of protein kinase A, PKA), or carbenoxolone (an inhibitor of gap junctions) reduced the frequency of the unstimulated, spontaneous and/or 5-HT-stimulated crop contractions. Adding aedeskinin III did not detectably alter crop contraction rates. In addition to pharmacological evidence of gap junctions, we demonstrated that the crop expressed several mRNAs encoding gap junctional proteins (i.e. innexins). Furthermore, we localized immunoreactivity for innexin 2 and innexin 3 to muscle and epithelial cells of the crop, respectively. Our results 1) suggest that 5-HT and myosupressins oppositely regulate contractile activity of the mosquito crop, and 2) provide the first evidence for putative roles of cAMP, PKA, and gap junctions in modulating contractile activity of the dipteran crop.
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Affiliation(s)
- Travis L Calkins
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA
| | - Andrew DeLaat
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA
| | - Peter M Piermarini
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA.
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Retinal gap junctions are involved in rhythmogenesis of neuronal activity at remote locations – Study on infra-slow oscillations in the rat olivary pretectal nucleus. Neuroscience 2016; 339:150-161. [DOI: 10.1016/j.neuroscience.2016.09.039] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 09/21/2016] [Accepted: 09/21/2016] [Indexed: 12/21/2022]
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Kim YJ, Kim J, Kim YS, Shin B, Choo OS, Lee JJ, Choung YH. Connexin 43 Acts as a Proapoptotic Modulator in Cisplatin-Induced Auditory Cell Death. Antioxid Redox Signal 2016; 25:623-636. [PMID: 27122099 DOI: 10.1089/ars.2015.6412] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
AIMS Gap junction coupling is known to play a role in intercellular communication by the Good Samaritan effect or bystander effect. Nonjunctional connexins (Cxs) may also play certain gap junction-independent roles in cell death or survival. The purpose of the present study was to investigate the role of junctional and nonjunctional Cxs in ototoxic drug-induced auditory cell death by focusing on Cx43 in the cochlea. RESULTS Nonjunctional Cx43 conditions were prepared by low confluence culture (5 × 103/cm2) or a trafficking inhibitor, brefeldin A (BFA), in auditory cells, and short lengthened Cx43s with amino-terminal (NT; amino acids 1-256) or carboxy-terminal (CT; amino acids 257-382) were transfected into Cx-deficient HeLa cells to avoid gap junction formation. Knockdown of nonchannel Cx43 (small interfering RNA [siRNA]) inhibited Cis-diamminedichloroplatinum (cisplatin)-induced cell death regardless of gap junction formation; however, a gap junction blocker, 18 alpha-glycyrrhetinic acid (18α-GA), showed inhibitory effect only under the junctional condition. BFA did not show any additive influence on the inhibitory effect of siRNA Cx43. Shortened Cx43-transfected HeLa cells also resulted in a significant increase in cell death under cisplatin. In the animal studies with cisplatin-treated rats, hearing thresholds of auditory brainstem response were significantly preserved by a gap junction blocker, carbenoxolone, showing much more preserved stereocilia of hair cells in scanning electron microscopic findings. Innovation and Conclusion: Cx43 plays a proapoptotic role in cisplatin-induced auditory cell death in both junctional and nonjunctional conditions. Targeting the Cx-mediated signaling control may be helpful in designing new therapeutic strategies for drug-induced ototoxicity. Antioxid. Redox Signal. 25, 623-636.
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Affiliation(s)
- Yeon Ju Kim
- 1 Department of Otolaryngology, Ajou University School of Medicine , Suwon, Republic of Korea
| | - Jangho Kim
- 2 Department of Rural and Biosystems Engineering, Chonnam National University , Gwangju, Republic of Korea
| | - Young Sun Kim
- 1 Department of Otolaryngology, Ajou University School of Medicine , Suwon, Republic of Korea
| | - Beomyong Shin
- 3 Department of Medical Sciences, The Graduate School, Ajou University , Suwon, Republic of Korea
| | - Oak-Sung Choo
- 1 Department of Otolaryngology, Ajou University School of Medicine , Suwon, Republic of Korea
| | - Jong Joo Lee
- 1 Department of Otolaryngology, Ajou University School of Medicine , Suwon, Republic of Korea
| | - Yun-Hoon Choung
- 1 Department of Otolaryngology, Ajou University School of Medicine , Suwon, Republic of Korea.,3 Department of Medical Sciences, The Graduate School, Ajou University , Suwon, Republic of Korea
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Chiou KK, Rocks JW, Chen CY, Cho S, Merkus KE, Rajaratnam A, Robison P, Tewari M, Vogel K, Majkut SF, Prosser BL, Discher DE, Liu AJ. Mechanical signaling coordinates the embryonic heartbeat. Proc Natl Acad Sci U S A 2016; 113:8939-44. [PMID: 27457951 PMCID: PMC4987837 DOI: 10.1073/pnas.1520428113] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
In the beating heart, cardiac myocytes (CMs) contract in a coordinated fashion, generating contractile wave fronts that propagate through the heart with each beat. Coordinating this wave front requires fast and robust signaling mechanisms between CMs. The primary signaling mechanism has long been identified as electrical: gap junctions conduct ions between CMs, triggering membrane depolarization, intracellular calcium release, and actomyosin contraction. In contrast, we propose here that, in the early embryonic heart tube, the signaling mechanism coordinating beats is mechanical rather than electrical. We present a simple biophysical model in which CMs are mechanically excitable inclusions embedded within the extracellular matrix (ECM), modeled as an elastic-fluid biphasic material. Our model predicts strong stiffness dependence in both the heartbeat velocity and strain in isolated hearts, as well as the strain for a hydrogel-cultured CM, in quantitative agreement with recent experiments. We challenge our model with experiments disrupting electrical conduction by perfusing intact adult and embryonic hearts with a gap junction blocker, β-glycyrrhetinic acid (BGA). We find this treatment causes rapid failure in adult hearts but not embryonic hearts-consistent with our hypothesis. Last, our model predicts a minimum matrix stiffness necessary to propagate a mechanically coordinated wave front. The predicted value is in accord with our stiffness measurements at the onset of beating, suggesting that mechanical signaling may initiate the very first heartbeats.
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Affiliation(s)
- Kevin K Chiou
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104
| | - Jason W Rocks
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104
| | - Christina Yingxian Chen
- Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104
| | - Sangkyun Cho
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Koen E Merkus
- Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - Anjali Rajaratnam
- Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104
| | - Patrick Robison
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Manorama Tewari
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Kenneth Vogel
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Stephanie F Majkut
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Benjamin L Prosser
- Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104
| | - Dennis E Discher
- Molecular and Cell Biophysics Laboratory, University of Pennsylvania, Philadelphia, PA 19104
| | - Andrea J Liu
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104;
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Bell CL, Murray SA. Adrenocortical Gap Junctions and Their Functions. Front Endocrinol (Lausanne) 2016; 7:82. [PMID: 27445985 PMCID: PMC4925680 DOI: 10.3389/fendo.2016.00082] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 06/20/2016] [Indexed: 12/21/2022] Open
Abstract
Adrenal cortical steroidogenesis and proliferation are thought to be modulated by gap junction-mediated direct cell-cell communication of regulatory molecules between cells. Such communication is regulated by the number of gap junction channels between contacting cells, the rate at which information flows between these channels, and the rate of channel turnover. Knowledge of the factors regulating gap junction-mediated communication and the turnover process are critical to an understanding of adrenal cortical cell functions, including development, hormonal response to adrenocorticotropin, and neoplastic dedifferentiation. Here, we review what is known about gap junctions in the adrenal gland, with particular attention to their role in adrenocortical cell steroidogenesis and proliferation. Information and insight gained from electrophysiological, molecular biological, and imaging (immunocytochemical, freeze fracture, transmission electron microscopic, and live cell) techniques will be provided.
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Affiliation(s)
- Cheryl L. Bell
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Sandra A. Murray
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
- *Correspondence: Sandra A. Murray,
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Gigout S, Louvel J, Pumain R. Decrease of neocortical paired-pulse depression in GAERS and possible implication of gap junctions. Neurosci Lett 2015; 584:302-7. [PMID: 25450143 DOI: 10.1016/j.neulet.2014.10.047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Revised: 10/10/2014] [Accepted: 10/28/2014] [Indexed: 10/24/2022]
Abstract
Thalamocortical slices are widely used to study thalamocortical relationships and absence epilepsy. However, it is still not known whether (1) intracortical synaptic transmission, in particular neocortical paired-pulse depression (PPD), is maintained in these slices and (2) whether PPD is altered in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS, a model of absence epilepsy for which cortico-thalamic loops are involved). Furthermore, while the involvement of gap junctions (GJ) in the mechanisms leading to epileptiform discharges has been intensively studied, little is known about their effect on intracortical transmission. We first studied intracortical connection efficacy and PPD in thalamocortical slices from GAERS and non-epileptic rats (NER). We then investigated the effects of GJ blockers (carbenoxolone and quinidine) on intracortical response following single or paired-pulse stimulations in coronal slices from Wistar rats. We show that the efficacy of intracortical connections is not impaired in GAERS. We also show that neocortical PPD is preserved in thalamocortical slices of NER, but that its efficacy is strongly decreased in GAERS. Moreover, a NMDA antagonist strongly reduced the PPD in NER but had no effect in GAERS. Cortical responses to white matter stimulation were not modified by quinidine or carbenoxolone in coronal slices of Wistar rats. PPD was recorded in these slices and was decreased by carbenoxolone but not by quinidine. We hypothesize that the decrease of PPD observed in GAERS might be due to a decrease in function of (1) NMDA receptors and/or (2) astrocytic GJ's.
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Affiliation(s)
- Sylvain Gigout
- INSERM U1129 "Infantile Epilepsies and Brain Plasticity", Paris, France; University Paris Descartes, Sorbonne Paris Cité; CEA, Gif sur Yvette, France.
| | - Jacques Louvel
- INSERM U1129 "Infantile Epilepsies and Brain Plasticity", Paris, France; University Paris Descartes, Sorbonne Paris Cité; CEA, Gif sur Yvette, France
| | - René Pumain
- INSERM U1129 "Infantile Epilepsies and Brain Plasticity", Paris, France; University Paris Descartes, Sorbonne Paris Cité; CEA, Gif sur Yvette, France
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10
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Connexins in migration during development and cancer. Dev Biol 2014; 401:143-51. [PMID: 25553982 DOI: 10.1016/j.ydbio.2014.12.023] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 12/17/2014] [Accepted: 12/18/2014] [Indexed: 12/12/2022]
Abstract
Connexins, the gap junction proteins, through their multitude of actions are implicated in a variety of cell processes during animal development and cancer. They allow direct or paracrine/autocrine cell communication through their channel and hemi-channel functions. They enable adhesion and interact with a plethora of signalling molecules. Here, we review the common themes in developmental and pathological processes and we focus in their involvement in cell migration in four different systems: neurons, astrocytes, neural crest and cancer.
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Palacios-Muñoz A, Escobar MJ, Vielma A, Araya J, Astudillo A, Valdivia G, García IE, Hurtado J, Schmachtenberg O, Martínez AD, Palacios AG. Role of connexin channels in the retinal light response of a diurnal rodent. Front Cell Neurosci 2014; 8:249. [PMID: 25202238 PMCID: PMC4142540 DOI: 10.3389/fncel.2014.00249] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Accepted: 08/05/2014] [Indexed: 01/02/2023] Open
Abstract
Several studies have shown that connexin channels play an important role in retinal neural coding in nocturnal rodents. However, the contribution of these channels to signal processing in the retina of diurnal rodents remains unclear. To gain insight into this problem, we studied connexin expression and the contribution of connexin channels to the retinal light response in the diurnal rodent Octodon degus (degu) compared to rat, using in vivo ERG recording under scotopic and photopic light adaptation. Analysis of the degu genome showed that the common retinal connexins present a high degree of homology to orthologs expressed in other mammals, and expression of Cx36 and Cx43 was confirmed in degu retina. Cx36 localized mainly to the outer and inner plexiform layers (IPLs), while Cx43 was expressed mostly in cells of the retinal pigment epithelium. Under scotopic conditions, the b-wave response amplitude was strongly reduced by 18-β-glycyrrhetinic acid (β-GA) (−45.1% in degu, compared to −52.2% in rat), suggesting that connexins are modulating this response. Remarkably, under photopic adaptation, β-GA increased the ERG b-wave amplitude in degu (+107.2%) while reducing it in rat (−62.3%). Moreover, β-GA diminished the spontaneous action potential firing rate in ganglion cells (GCs) and increased the response latency of ON and OFF GCs. Our results support the notion that connexins exert a fine-tuning control of the retinal light response and have an important role in retinal neural coding.
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Affiliation(s)
- Angelina Palacios-Muñoz
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Maria J Escobar
- Departamento de Electrónica, Universidad Técnico Federico Santa María Valparaíso, Chile
| | - Alex Vielma
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Joaquín Araya
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Aland Astudillo
- Departamento de Electrónica, Universidad Técnico Federico Santa María Valparaíso, Chile
| | - Gonzalo Valdivia
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Isaac E García
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - José Hurtado
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile ; Instituto de Sistemas Complejos de Valparaíso Valparaíso, Chile
| | - Oliver Schmachtenberg
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Agustín D Martínez
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Adrian G Palacios
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile ; Instituto de Sistemas Complejos de Valparaíso Valparaíso, Chile
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12
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Mandel K, Yang Y, Schambach A, Glage S, Otte A, Hass R. Mesenchymal stem cells directly interact with breast cancer cells and promote tumor cell growth in vitro and in vivo. Stem Cells Dev 2013; 22:3114-27. [PMID: 23895436 DOI: 10.1089/scd.2013.0249] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cellular interactions were investigated between human mesenchymal stem cells (MSC) and human breast cancer cells. Co-culture of the two cell populations was associated with an MSC-mediated growth stimulation of MDA-MB-231 breast cancer cells. A continuous expansion of tumor cell colonies was progressively surrounded by MSC(GFP) displaying elongated cell bodies. Moreover, some MSC(GFP) and MDA-MB-231(cherry) cells spontaneously generated hybrid/chimeric cell populations, demonstrating a dual (green fluorescent protein+cherry) fluorescence. During a co-culture of 5-6 days, MSC also induced expression of the GPI-anchored CD90 molecule in breast cancer cells, which could not be observed in a transwell assay, suggesting the requirement of direct cellular interactions. Indeed, MSC-mediated CD90 induction in the breast cancer cells could be partially blocked by a gap junction inhibitor and by inhibition of the notch signaling pathway, respectively. Similar findings were observed in vivo by which a subcutaneous injection of a co-culture of primary MSC with MDA-MB-231(GFP) cells into NOD/scid mice exhibited an about 10-fold increased tumor size and enhanced metastatic capacity as compared with the MDA-MB-231(GFP) mono-culture. Flow cytometric evaluation of the co-culture tumors revealed more than 90% of breast cancer cells with about 3% of CD90-positive cells, also suggesting an MSC-mediated in vivo induction of CD90 in MDA-MB-231 cells. Furthermore, immunohistochemical analysis demonstrated an elevated neovascularization and viability in the MSC/MDA-MB-231(GFP)-derived tumors. Together, these data suggested an MSC-mediated growth stimulation of breast cancer cells in vitro and in vivo by which the altered MSC morphology and the appearance of hybrid/chimeric cells and breast cancer-expressing CD90(+) cells indicate mutual cellular alterations.
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Affiliation(s)
- Katharina Mandel
- 1 Biochemistry and Tumor Biology Lab, Gynecology Research Unit , Department of Obstetrics and Gynecology, Hannover Medical School, Hannover, Germany
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13
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Kotak VC, Péndola LM, Rodríguez-Contreras A. Spontaneous activity in the developing gerbil auditory cortex in vivo involves GABAergic transmission. Neuroscience 2012; 226:130-44. [PMID: 22986170 DOI: 10.1016/j.neuroscience.2012.09.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2011] [Revised: 09/04/2012] [Accepted: 09/04/2012] [Indexed: 10/27/2022]
Abstract
A salient feature of the developing brain is that spontaneous oscillations (SOs) and waves may influence the emergence of synaptic connections. While GABA produces depolarization and may support SOs in the neurons of developing rodents, it elicits hyperpolarization and diminishes SOs in developing gerbil auditory cortex (ACx). Therefore, we asked whether SOs exist in developing gerbil ACx in vivo and if GABAergic involvement can be manipulated. In vivo extracellular recordings in P3-5 ACx revealed SOs with longer burst durations and shorter inter-event intervals compared to ACx SOs in slices. ACx was then validated by gross anatomical features and lesions created at the in vivo recording site that corresponded with the electrophysiological coordinates of thalamorecipient ACx in slices. Further, NeuroVue Red, a lipophilic dye loaded at the in vivo recording sites, stained anatomically identifiable fiber tracks between the ACx and the auditory thalamus, medial geniculate body (MG). Separately, to chronically perturb GABAergic role in SOs, P2-5 pups were administered daily with GABA(A) receptor blocker, bicuculline (BIC). We then recorded from P14-17 ACx neurons in slices generated after hearing onset. ACx neurons from BIC-administered pups exhibited spontaneous action potentials in contrast to subthreshold synaptic potentials in neurons from sham-injected animals. Finally, to elucidate whether the gap junction blocker mefloquine (MFQ) previously shown to dampen ACx SOs in slices affected GABAergic transmission, MFQ was acutely applied in P3-5 slices while spontaneous inhibitory postsynaptic currents (sIPSCs) were recorded. Whereas MFQ increased the amplitude and frequency of sIPSCs in ACx neurons, the broad-spectrum gap junction blocker carbenoxolone decreased sIPSC amplitudes only. Together, we show that P2-5 gerbil ACx can endogenously generate SOs in vivo. Persistence of activity in ACx in P14-17 slices from pups administered with BIC at P2-5 implies that inhibitory GABAergic activity linked with gap-junction participates in the maturation of ACx.
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Affiliation(s)
- V C Kotak
- Center for Neural Science, 4 Washington Place, New York, NY 10003, USA.
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14
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Klaassen LJ, Fahrenfort I, Kamermans M. Connexin hemichannel mediated ephaptic inhibition in the retina. Brain Res 2012; 1487:25-38. [PMID: 22796289 DOI: 10.1016/j.brainres.2012.04.059] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Accepted: 04/11/2012] [Indexed: 11/25/2022]
Abstract
Connexins are the building blocks of gap-junctions; sign conserving electrical synapses. Recently it has been shown that connexins can also function as hemichannels and can mediate a sign inverting inhibitory synaptic signal from horizontal cells to cones via an ephaptic mechanism. In this review we will discuss the critical requirements for such an ephaptic interaction and relate these to the available experimental evidence. The highly conserved morphological structure of the cone synapse together with a number of specific connexin proteins and proteoglycans present in the synaptic complex of the cones creates a synaptic environment that allows ephaptic interactions. The connexins involved are members of a special group of connexins, encoded by the GJA9 and GJA10 genes. Surprisingly, in contrast to many other vertebrates, mouse and other rodents seem to lack a GJA9 encoded connexin. The specific combination of substances that block feedback and the highly specific modification of feedback in a zebrafish lacking Cx55.5 hemichannels all point to an ephaptic feedback mechanism from horizontal cells to cones. This article is part of a Special Issue entitled Electrical Synapses.
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Affiliation(s)
- Lauw J Klaassen
- The Netherlands Institute for Neuroscience, Department of Retinal Signal Processing, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands
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15
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Trenholm S, Borowska J, Zhang J, Hoggarth A, Johnson K, Barnes S, Lewis TJ, Awatramani GB. Intrinsic oscillatory activity arising within the electrically coupled AII amacrine-ON cone bipolar cell network is driven by voltage-gated Na+ channels. J Physiol 2012; 590:2501-17. [PMID: 22393249 DOI: 10.1113/jphysiol.2011.225060] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In the rd1 mouse model for retinal degeneration, the loss of photoreceptors results in oscillatory activity (∼10–20 Hz) within the remnant electrically coupled network of retinal ON cone bipolar and AII amacrine cells. We tested the role of hyperpolarization-activated currents (I(h)), voltage-gated Na(+) channels and gap junctions in mediating such oscillatory activity. Blocking I(h) (1 mm Cs(+)) hyperpolarized the network and augmented activity, while antagonizing voltage-dependent Na(+) channels (1 μm TTX) abolished oscillatory activity in the AII amacrine-ON cone bipolar cell network. Voltage-gated Na(+) channels were only observed in AII amacrine cells, implicating these cells as major drivers of activity. Pharmacologically uncoupling the network (200 μm meclofenamic acid (MFA)) blocked oscillations in all cells indicating that Na(+) channels exert their influence over multiple cell types within the network. In wt retina, occluding photoreceptor inputs to bipolar cells (10 μm NBQX and 50 μm l-AP4) resulted in a mild (∼10 mV) hyperpolarization and the induction of oscillatory activity within the AII amacrine-ON cone bipolar cell network. These oscillations had similar properties to those observed in rd1 retina, suggesting that no major degeneration-induced network rewiring is required to trigger spontaneous oscillations. Finally, we constructed a simplified computational model that exhibited Na(+) channel-dependent network oscillations. In this model, mild heterogeneities in channel densities between individual neurons reproduced our experimental findings. These results indicate that TTX-sensitive Na(+) channels in AII amacrine cells trigger degeneration-induced network oscillations, which provide a persistent synaptic drive to downstream remnant neurons, thus appearing to replace photoreceptors as the principal drivers of retinal activity.
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Affiliation(s)
- Stuart Trenholm
- Department of Anatomy, Dalhousie University, Halifax, NS, Canada B3H 1X5
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16
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Deniz S, Wersinger E, Schwab Y, Mura C, Erdelyi F, Szabó G, Rendon A, Sahel JA, Picaud S, Roux MJ. Mammalian retinal horizontal cells are unconventional GABAergic neurons. J Neurochem 2010; 116:350-62. [PMID: 21091475 DOI: 10.1111/j.1471-4159.2010.07114.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Lateral interactions at the first retinal synapse have been initially proposed to involve GABA by transporter-mediated release from horizontal cells, onto GABA(A) receptors expressed on cone photoreceptor terminals and/or bipolar cell dendrites. However, in the mammalian retina, horizontal cells do not seem to contain GABA systematically or to express membrane GABA transporters. We here report that mouse retinal horizontal cells express GAD65 and/or GAD67 mRNA, and were weakly but consistently immunostained for GAD65/67. While GABA was readily detected after intracardiac perfusion, it was lost during classical preparation for histology or electrophysiology. It could not be restored by incubation in a GABA-containing medium, confirming the absence of membrane GABA transporters in these cells. However, GABA was synthesized de novo from glutamate or glutamine, upon addition of pyridoxal 5'-phosphate, a cofactor of GAD65/67. Mouse horizontal cells are thus atypical GABAergic neurons, with no functional GABA uptake, but a glutamate and/or glutamine transport system allowing GABA synthesis, probably depending physiologically from glutamate released by photoreceptors. Our results suggest that the role of GABA in lateral inhibition may have been underestimated, at least in mammals, and that tissue pre-incubation with glutamine and pyridoxal 5'-phosphate should yield a more precise estimate of outer retinal processing.
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Affiliation(s)
- Sercan Deniz
- Department of Neurobiology and Genetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS UMR_7104, Inserm U 964, Université de Strasbourg, Illkirch, France
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17
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Veruki ML, Hartveit E. Meclofenamic acid blocks electrical synapses of retinal AII amacrine and on-cone bipolar cells. J Neurophysiol 2009; 101:2339-47. [PMID: 19279153 DOI: 10.1152/jn.00112.2009] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gap junction channels constitute specialized intercellular contacts that can serve as electrical synapses. In the rod pathway of the retina, electrical synapses between AII amacrine cells express connexin 36 (Cx36) and electrical synapses between AII amacrines and on-cone bipolar cells express Cx36 on the amacrine side and Cx36 or Cx45 on the bipolar side. For physiological investigations of the properties and functions of these electrical synapses, it is highly desirable to have access to potent pharmacological blockers with selective and reversible action. Here we use dual whole cell voltage-clamp recordings of pairs of AII amacrine cells and pairs of AII amacrine and on-cone bipolar cells in rat retinal slices to directly measure the junctional conductance (G(j)) between electrically coupled cells and to study the effect of the drug meclofenamic acid (MFA) on G(j). Consistent with previous tracer coupling studies, we found that MFA reversibly blocked the electrical synapse currents in a concentration-dependent manner, with complete block at 100 muM. Whereas MFA evoked a detectable decrease in G(j) within minutes of application, the time to complete block of G(j) was considerably longer, typically 20-40 min. After washout, G(j) recovered to 20-90% of the control level, but the time to maximum recovery was typically >1 h. These results suggest that MFA can be a useful drug to investigate the physiological functions of electrical synapses in the rod pathway, but that the slow kinetics of block and reversal might compromise interpretation of the results and that explicit monitoring of G(j) is desirable.
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Affiliation(s)
- Margaret Lin Veruki
- University of Bergen, Department of Biomedicine, Jonas Lies vei 91, N-5009 Bergen, Norway
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18
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Disinhibition combines with excitation to extend the operating range of the OFF visual pathway in daylight. J Neurosci 2008; 28:4136-50. [PMID: 18417693 DOI: 10.1523/jneurosci.4274-07.2008] [Citation(s) in RCA: 181] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cone signals divide into parallel ON and OFF bipolar cell pathways, which respond to objects brighter or darker than the background and release glutamate onto the corresponding type of ganglion cell. It is assumed that ganglion cell excitatory responses are driven by these bipolar cell synapses. Here, we report an additional mechanism: OFF ganglion cells were driven in part by the removal of synaptic inhibition (disinhibition). The disinhibition played a relatively large role in driving responses at low contrasts. The disinhibition persisted in the presence of CNQX and d-AP-5. Furthermore, the CNQX/d-AP-5-resistant response was blocked by l-AP-4, meclofenamic acid, quinine, or strychnine but not by bicuculline. Thus, the disinhibition circuit was driven by the ON pathway and required gap junctions and glycine receptors but not ionotropic glutamate or GABA(A) receptors. These properties implicate the AII amacrine cell, better known for its role in rod vision, as a critical circuit element through the following pathway: cone --> ON cone bipolar cell --> AII cell --> OFF ganglion cell. Rods could also drive this circuit through their gap junctions with cones. Thus, to light decrement, AII cells, driven by electrical synapses with ON cone bipolar cells, would hyperpolarize and reduce glycine release to excite OFF ganglion cells. To light increment, the AII circuit would directly inhibit OFF ganglion cells. These results show a new role for disinhibition in the retina and suggest a new role for the AII amacrine cell in daylight vision.
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19
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Dedek K, Pandarinath C, Alam NM, Wellershaus K, Schubert T, Willecke K, Prusky GT, Weiler R, Nirenberg S. Ganglion cell adaptability: does the coupling of horizontal cells play a role? PLoS One 2008; 3:e1714. [PMID: 18320035 PMCID: PMC2246161 DOI: 10.1371/journal.pone.0001714] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Accepted: 02/04/2008] [Indexed: 11/19/2022] Open
Abstract
Background The visual system can adjust itself to different visual environments. One of the most well known examples of this is the shift in spatial tuning that occurs in retinal ganglion cells with the change from night to day vision. This shift is thought to be produced by a change in the ganglion cell receptive field surround, mediated by a decrease in the coupling of horizontal cells. Methodology/Principal Findings To test this hypothesis, we used a transgenic mouse line, a connexin57-deficient line, in which horizontal cell coupling was abolished. Measurements, both at the ganglion cell level and the level of behavioral performance, showed no differences between wild-type retinas and retinas with decoupled horizontal cells from connexin57-deficient mice. Conclusion/Significance This analysis showed that the coupling and uncoupling of horizontal cells does not play a dominant role in spatial tuning and its adjustability to night and day light conditions. Instead, our data suggest that another mechanism, likely arising in the inner retina, must be responsible.
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Affiliation(s)
- Karin Dedek
- Department of Neurobiology, University of Oldenburg, Oldenburg, Germany
| | - Chethan Pandarinath
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York, United States of America
| | - Nazia M. Alam
- Canadian Centre for Behavioural Neuroscience, The University of Lethbridge, Lethbridge, Alberta, Canada
| | | | - Timm Schubert
- Department of Neurobiology, University of Oldenburg, Oldenburg, Germany
| | - Klaus Willecke
- Institute of Genetics, University of Bonn, Bonn, Germany
| | - Glen T. Prusky
- Canadian Centre for Behavioural Neuroscience, The University of Lethbridge, Lethbridge, Alberta, Canada
| | - Reto Weiler
- Department of Neurobiology, University of Oldenburg, Oldenburg, Germany
| | - Sheila Nirenberg
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York, United States of America
- *E-mail:
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20
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Pan F, Mills SL, Massey SC. Screening of gap junction antagonists on dye coupling in the rabbit retina. Vis Neurosci 2007; 24:609-18. [PMID: 17711600 PMCID: PMC2213422 DOI: 10.1017/s0952523807070472] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2007] [Accepted: 05/11/2007] [Indexed: 11/07/2022]
Abstract
Many cell types in the retina are coupled via gap junctions and so there is a pressing need for a potent and reversible gap junction antagonist. We screened a series of potential gap junction antagonists by evaluating their effects on dye coupling in the network of A-type horizontal cells. We evaluated the following compounds: meclofenamic acid (MFA), mefloquine, 2-aminoethyldiphenyl borate (2-APB), 18-alpha-glycyrrhetinic acid, 18-beta-glycyrrhetinic acid (18-beta-GA), retinoic acid, flufenamic acid, niflumic acid, and carbenoxolone. The efficacy of each drug was determined by measuring the diffusion coefficient for Neurobiotin (Mills & Massey, 1998). MFA, 18-beta-GA, 2-APB and mefloquine were the most effective antagonists, completely eliminating A-type horizontal cell coupling at a concentration of 200 muM. Niflumic acid, flufenamic acid, and carbenoxolone were less potent. Additionally, carbenoxolone was difficult to wash out and also may be harmful, as the retina became opaque and swollen. MFA, 18-beta-GA, 2-APB and mefloquine also blocked coupling in B-type horizontal cells and AII amacrine cells. Because these cell types express different connexins, this suggests that the antagonists were relatively non-selective across several different types of gap junction. It should be emphasized that MFA was water-soluble and its effects on dye coupling were easily reversible. In contrast, the other gap junction antagonists, except carbenoxolone, required DMSO to make stock solutions and were difficult to wash out of the preparation at the doses required to block coupling in A-type HCs. The combination of potency, water solubility and reversibility suggest that MFA may be a useful compound to manipulate gap junction coupling.
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Affiliation(s)
- Feng Pan
- Department of Ophthalmology and Visual Science, University of Texas Medical School at Houston, Houston, Texas 77030, USA
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21
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Lee IK, Rhee SK. Inhibitory effect of bisphenol A on gap junctional intercellular communication in an epithelial cell line of rat mammary tissue. Arch Pharm Res 2007; 30:337-43. [PMID: 17424940 DOI: 10.1007/bf02977615] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
An endocrine disruptor, bisphenol-A (BPA), has been reported to have several short-term actions in various cells and tissues. However, the mechanisms of these actions have not been fully elucidated. In order to assess the effect of BPA on the intercellular communication mediated by gap junctions, we conducted the present study in the rat epithelium-derived BICR-M1Rk cell-line, in which connexin 43 (Cx43) is a major gap junction channel-forming protein. The cytotoxicity of BPA toward the cultured cells was evaluated by using both MTT reduction and LDH leakage assay systems. The results showed no appreciable loss in cell viability in the presence of increasing concentrations of BPA (from 0.1 to 3.2 microM) for 1 h incubation. However, most of cell viability was lost when cells were incubated for 24 hr with the same concentrations of BPA. The BPA acted as an antagonist on gap junction-mediated intercellular communication (GJIC), and the phenomenon was dose-dependent and irreversible. According to the data obtained from scrape-loading dye-transfer experiments, three quarters of normal GJIC was reduced by concentration of 0.4 microM BPA for 1 h incubation. To identify the relevance of this retardation upon BPA treatment, the GJIC to Cx43 synthesis, the mRNA and protein levels of Cx43 were assessed with RT-PCR and Western-blotting, respectively. The total protein level of Cx43 was almost constant in a wide range of BPA concentrations, as well as in Cx43 mRNA level. These results suggest that BPA inhibits GJIC through a modulation of the gating of gap junction channels, not through a genomic modulation of Cx43.
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Affiliation(s)
- In-Kyoung Lee
- Institute of Natural Sciences Yeungnam University, Kyongsan 712-749, Korea
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22
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Hornstein EP, Verweij J, Li PH, Schnapf JL. Gap-junctional coupling and absolute sensitivity of photoreceptors in macaque retina. J Neurosci 2006; 25:11201-9. [PMID: 16319320 PMCID: PMC6725652 DOI: 10.1523/jneurosci.3416-05.2005] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We investigated gap-junctional coupling of rods and cones in macaque retina. Cone voltage responses evoked by light absorption in neighboring rods were briefer and smaller than responses recorded in the rods themselves. Rod detection thresholds, calculated from noise and response amplitude histograms, closely matched the threshold for an ideal detector limited by quantal fluctuations in the stimulus. Surprisingly, cone thresholds were only approximately two times higher. Amplitude fluctuations in cones could be explained by a Poisson distribution of photoisomerizations within a pool of seven or more coupled rods. Neurobiotin coupling between rods and cones was consistent with our electrical recordings, with approximately six rods labeled per injected cone. The spatial distribution of tracer-coupled rods matched the light-evoked cone receptive field. The gap junction inhibitor carbenoxolone abolished both electrical and tracer coupling. Amplitude fluctuations in most rods were accounted for by the expected rate of light absorption in their outer segments. The fluctuations in some rods, however, were consistent with a summation pool of up to six rods. When single rods were injected with Neurobiotin, up to 10 rods were labeled. Rod-rod and rod-cone electrical coupling is expected to extend the range of scotopic vision by circumventing saturation at the rod to rod-bipolar cell synapse; however, because coupling also renders the rod synapse less effective at separating out photon signals from dark noise, coupling is expected to elevate the absolute threshold of dark-adapted observers.
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Affiliation(s)
- Eric P Hornstein
- Department of Ophthalmology, University of California, San Francisco, California 94143-0730, USA
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23
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Striedinger K, Petrasch-Parwez E, Zoidl G, Napirei M, Meier C, Eysel UT, Dermietzel R. Loss of connexin36 increases retinal cell vulnerability to secondary cell loss. Eur J Neurosci 2005; 22:605-16. [PMID: 16101742 DOI: 10.1111/j.1460-9568.2005.04228.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Accruing evidence indicates that gap junctions are involved in neuronal survival after brain injury. The present study was aimed at clarifying the contribution of the neuronal gap-junction protein connexin36 (Cx36) to secondary cell loss after injury in the mouse retina. A focal retinal lesion was induced by infrared laser photocoagulation. Remarkably, this model allowed spatial and temporal definition of the lesion with high reproducibility. Moreover, Cx36 is abundantly expressed in the retina and plays an essential role in the visual transmission process. Taking advantage of these features, cell death was assessed using TUNEL assay and light and electron microscopy, and the extent of Cx36 expression was studied by immunohistochemistry, Western blot, in situ hybridization and real-time RT-PCR. Secondary cell loss was most prominent between 24 and 48 h after lesioning. This peak was accompanied by an increase in Cx36 expression. When cultured explanted retinas were subjected to gap-junction blockers a significant increase in the extent of secondary cell loss after laser photocoagulation became evident. Using the same experimental paradigm we compared the incidence of cell death in wild-type and Cx36(-/-) mice. A significant increase in total number of TUNEL-positive cells occurred in the Cx36(-/-) mice compared to controls. From these data we conclude that Cx36 contributes to the survival and resistance against damage of retinal cells and thus constitutes a protective factor after traumatic injury of the retina.
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Affiliation(s)
- Katharine Striedinger
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University, Universitätstrasse 150, D-44801 Bochum, Germany
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24
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Contreras JE, Sánchez HA, Véliz LP, Bukauskas FF, Bennett MV, Sáez JC. Role of connexin-based gap junction channels and hemichannels in ischemia-induced cell death in nervous tissue. ACTA ACUST UNITED AC 2005; 47:290-303. [PMID: 15572178 PMCID: PMC3651737 DOI: 10.1016/j.brainresrev.2004.08.002] [Citation(s) in RCA: 182] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/27/2004] [Indexed: 01/24/2023]
Abstract
Gap junction channels and hemichannels formed of connexin subunits are found in most cell types in vertebrates. Gap junctions connect cells via channels not open to the extracellular space and permit the passage of ions and molecules of approximately 1 kDa. Single connexin hemichannels, which are connexin hexamers, are present in the surface membrane before docking with a hemichannel in an apposed membrane. Because of their high conductance and permeability in cell-cell channels, it had been thought that connexin hemichannels remained closed until docking to form a cell-cell channel. Now it is clear that at least some hemichannels can open to allow passage of molecules between the cytoplasm and extracellular space. Here we review evidence that gap junction channels may allow intercellular diffusion of necrotic or apoptotic signals, but may also allow diffusion of ions and substances from healthy to injured cells, thereby contributing to cell survival. Moreover, opening of gap junction hemichannels may exacerbate cell injury or mediate paracrine or autocrine signaling. In addition to the cell specific features of an ischemic insult, propagation of cell damage and death within affected tissues may be affected by expression and regulation of gap junction channels and hemichannels formed by connexins.
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Affiliation(s)
- Jorge E. Contreras
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
| | - Helmuth A. Sánchez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
- Corresponding author. Tel.: +56 2 6862860; fax: +56 2 2225515. (H.A. Sánchez)
| | - Loreto P. Véliz
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
| | | | - Michael V.L. Bennett
- Department of Neurosciences, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Juan C. Sáez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
- Department of Neurosciences, Albert Einstein College of Medicine, Bronx, NY, USA
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25
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Chappell RL, Qian H, Zakevicius J, Ripps H. Histidine suppresses zinc modulation of connexin hemichannels. THE BIOLOGICAL BULLETIN 2004; 207:188-190. [PMID: 15616348 DOI: 10.2307/1543206] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
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26
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Kamermans M, Fahrenfort I. Ephaptic interactions within a chemical synapse: hemichannel-mediated ephaptic inhibition in the retina. Curr Opin Neurobiol 2004; 14:531-41. [PMID: 15464885 DOI: 10.1016/j.conb.2004.08.016] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The two best-known types of cell-cell communication are chemical synapses and electrical synapses, which are formed by gap junctions. A third, less well known, form of communication is ephaptic transmission, in which electric fields generated by a specific neuron alter the excitability of neighboring neurons as a result of their anatomical and electrical proximity. Ephaptic communication can be present in a variety of forms, each with their specific features and functional implications. One of these is ephaptic modulation within a chemical synapse. This type of communication has recently been proposed for the cone-horizontal cell synapse in the vertebrate retina. Evidence indicates that the extracellular potential in the synaptic terminal of photoreceptors is modulated by current flowing through connexin hemichannels at the tips of the horizontal cell dendrites, mediating negative feedback from horizontal cells to cones. This example can be added to the growing list of cases of ephaptic communication in the central nervous system.
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Affiliation(s)
- Maarten Kamermans
- The Netherlands Ophthalmic Research Institute, Royal Netherlands Academy of Arts and Sciences, Meiberdreef 47, 1105 BA Amsterdam, The Netherlands.
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Vessey JP, Lalonde MR, Mizan HA, Welch NC, Kelly MEM, Barnes S. Carbenoxolone inhibition of voltage-gated Ca channels and synaptic transmission in the retina. J Neurophysiol 2004; 92:1252-6. [PMID: 15028741 DOI: 10.1152/jn.00148.2004] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We show that carbenoxolone, a drug used to block hemichannels in the retina to test the ephaptic model of horizontal cell inhibitory feedback, has strong inhibitory effects on voltage-gated Ca channels. Carbenoxolone (100 microM) reduced photoreceptor-to-horizontal cell synaptic transmission by 92%. Applied to patch-clamped, isolated cone photoreceptors, carbenoxolone inhibited Ca channels with an EC(50) of 48 microM. At 100 microM, it reduced cone Ca channel current by 37%, reduced depolarization-evoked [Ca(2+)] signals in fluo-4 loaded retinal slices by 57% and inhibited Ca channels in Müller cells by 52%. A synaptic transfer model suggests that the degree of block of Ca channels accounts for the reduction in synaptic transmission. These results suggest broad inhibitory actions for carbenoxolone in the retina that must be considered when interpreting its effects on inhibitory feedback.
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Affiliation(s)
- John P Vessey
- Department of Physiology and Biophysics, Dalhousie University, 5859 University Ave., Halifax, Nova Scotia B3H-4H7, Canada
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